Your patient spent December trying to ward off pain in bed or that comfortable (read: ugly) recliner.

He finally gave up and decided to bite the bullet and have that hip surgery his doc had suggested a year ago.

The doctor warns: "It's going to be three months of just plain hard work."

But you have an idea that rehab isn't going to be quite as tough as it could be. Why? You've got a pool in your pocket and you know how to use it. Your patient gets the best that therapy can offer: both land and water.

Rationale for Use of Water
There is no question that the water offers a therapeutic environment which can be harnessed by a skilled therapist to permit activities for the postoperative patient. This environment is created because of the unique properties of water and it is both difficult and clinically impractical to achieve a similar environment on land. Take a moment to examine these properties one-by-one.

Buoyancy
Archimedes' principle (oh why do these aquatic articles always invoke Archimedes?) states: "when a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of fluid displaced."

OK. So what? In a nutshell, this upthrust, or buoyancy can be used to provide either assistance or resistance to movement of the body. It all depends on the position of the patient's body.

The human body has elements which tend to sink (dense muscle) and elements which tend to float (fatty tissue and air-filled lungs). This tendency to float counterbalances gravity and supports the body, resulting in an apparent reduction in weight.

This reduction in weight can provide relief from compressive forces on painful joints. It is therefore possible for the postoperative patient to stand, even walk, with reduced pain without external support or abnormal protective mechanisms in the water.

Thus, the patient can initiate "normal" weight bearing tasks such as gait, transfers, and balance drills immediately after surgery and offset any deconditioning effects of immobility or reduced movement.

Even better? This reduction in compression creates an environment in which weight bearing and joint compression can be applied in a graded or progressive manner by the therapist. Weight bearing may be systematically reduced by increasing the amount of the body submerged.

Static (standing) immersion at the level of the anterior superior iliac spine (ASIS) reduces weight 40%-56% of normal. Be careful though: all bets are off when the patient moves. During slow walking, patients must be immersed to the clavicle to reduce weight bearing to 50%, and during fast walking, patients must be immersed deeper than the xiphosternum in order to reduce weight that much.

In conclusion, buoyancy can be used to create:

• A decrease in weight bearing through joints;
• A decrease in joint stress;
• A decrease in splinting or guarding of antigravity muscles;
• An increase in freedom of movement.

Buoyancy can also promote ease of handling of the large or heavy patient and allow access to body parts which would be inaccessible if the patient was positioned on a plinth or chair.

Hydrostatic Pressure
Pascal's Law states that "Fluid pressure is exerted equally on all surfaces of an immersed body at rest at a given depth".

In essence, hydrostatic pressure increases the pressure on the outside of an immersed standing body, resulting in:

• A reduction in edema in the lower extremities (by providing graduated pressure at greater depths);
• An offsetting of blood pooling in lower extremities (and thus a reduction in the risk for postoperative clotting);
• A desensitization effect (by constantly stimulating phasic receptors).

This means the postoperative patient can be relieved of some of the potential for swelling and clotting problems associated with surgery.

Viscosity
Viscosity is nothing more than the inherent friction that exists between molecules of a liquid which cause a resistance to flow. Water is more viscous than air , thus, it takes more force to push through water molecules than to push through air molecules.

Additionally, the faster an object is pushed through the water, the more turbulence is created and this creates additional resistance to movement.Keep in mind that the postoperative patient has probably already lost a great deal of proprioception for a number of reasons.

First, his joint has been worn-down, perhaps to bone-on-bone and has lost its normal weight-bearing feedback capacity.

Second, the joint is further traumatized by surgical intervention (perhaps even sacrificing additional Golgi tendon organs and muscle spindles to the surgeon's blade). It seems likely that movement in water can offer patients exaggerated input from the environment -- perhaps resulting in enhanced proprioception.

Flow
When an object moves through a fluid, there is an increase in the pressure in the front of an object combined with a reduction in pressure in the back. This results in the water wanting to move from an area of high pressure to an area of lower pressure.

The area of "negative pressure" is known as the wake. Eddy currents form in this wake and "drag" the object back. The negative pressure (or drag) behind a moving object (the wake) is responsible for 90% of the impedance of movement. Surprisingly, the bow wave (the positive pressure in front of the object) is only responsible for 10% of the impedance.

The principle of flow can be used therapeutically to increase (or decrease) the force necessary to push through the water. This property can be used to create a progressive resistive exercise program that is three-dimensional, velocity-specific, and safe to perform.

Refraction
Refraction is the prism effect that is evident when looking from an air medium to a water medium. Light bends when its rays move from a more dense to a less dense substance.

Most of the "therapeutic" effects of refraction are negative. Refraction decreases depth perception and makes the pool seems shallower. It alters visual cues for both patient and provider. Patient's limbs seem distorted (bent away), and items seem high and to the right, thus making visual feedback and monitoring is more difficult.

For the postoperative patient, it is possible to use refraction therapeutically. For instance, while immersed, a patient with a habitual visual method of joint placement (e.g. someone who looks at his feet to walk) may be forced to use his proprioceptive system instead.

Thermal Shifts
At temperatures above "thermoneutral" (approximately 93° Fahrenheit at rest), body temperature increases due to the reduced ability of the body to dissipate heat through the skin. Thermal energy (heat) is exchanged between water and the body and between air and the body.

Energy exchange between a submerged body and the water occurs through both convection and conduction. Thermal energy is also exchanged between the body and the air through radiation and evaporation -- methods which become more critical if the total body is immersed and the water temperature prevents heat dissipation from occurring during aquatic exercise.

Although dependent on the population using the facility, therapeutic pools are generally heated to between 92-97° Fahrenheit.

Immersion in water warmer than the skin will result in a rise in superficial tissue temperature which creates a palliative effect like that experienced during the therapeutic use of paraffin, Fluidotherapy® and moist heat.

Immersion in thermoneutral water will produce a generalized relaxation effect similar to that experienced with swaddling or bundling of a body part.

Special Considerations for the Patient who has Undergone Hip Surgery
Even though the water is an ideal environment to tackle many problems inherent in the postoperative population, there are still considerations of which the therapist must be aware. Take a moment to examine the following to ensure you will provide the best care to your patients with hip conditions.

Precautions and Contraindications
There are many potential precautions to consider for the s/p hip surgery patient. Here are several things to consider when taking this population into the pool:

• If the patient is uncomfortable or anxious in water, the resulting muscular bracing and splinting may make pain worse.
• If the patient has undergone total hip replacement surgery with a posterior approach, extreme caution must be taken to avoid contraindicated positions (hip internal rotation, adduction, and flexion above 90°). The freedom of movement possible in water may allow the patient to perform movements which should not be performed.
• If the patient has a surgical suture site or an open wound, a decision must when to permit the patient in the pool. This decision is based on a risk:benefit ratio. If the patient's skin is delicate and in danger of maceration, or if the wound is draining, there must be a very compelling reason (benefit) to taking the patient into the pool. If the wound is clean and healing and is covered with a bio-occlusive dressing (such as Tegaderm or Op-site), there is little risk involved in taking the patient into the pool so the benefit does not have to be as great. If the patient is immersed, care must be taken to thoroughly dry (via "patting" not rubbing) the surgical site after immersion.
• If the patient is incontinent of bowel, he must be on a bowel program before allowing him into the pool. Incontinence of urine is not a reason to disallow aquatic therapy.

Techniques and Specifics for Designing Programs
Therapists must treat the patient who has just undergone hip surgery carefully. There are many considerations when designing an aquatic therapy program for this population. For example:

• Start any new patient in water that is no deeper than he can comfortably stand. Remember that fear can contribute to muscle guarding which can increase pain. Provide equipment for buoyancy-assistance (such as an aqua-stick or a floatation barbell) so the patient does not require the assistance of the therapist to feel safe.
• Be sure to provide more warm-up time at the beginning of each treatment to allow injured/repaired joints to "warm up" (from the synovial fluid bathing the joint). Make sure you increase progressive resistive exercise (PRE) gradually to prevent delayed onset muscle soreness or dislocation of a new hip. Increase weight-bearing progressively by moving the patient shallower to return the patient to functional (land-based) status as soon as feasible.
• If at all possible, water temperature should be at least 93° Fahrenheit (thermoneutral) for pain palliation.
• Don't neglect aerobic conditioning in this population as there is a strong relationship between aerobic exercise and pain palliation. However, be sure the patient understands his target heart rate zone for aquatic exercise is at least 12 - 17 beats per minute lower than its land-based counterpart.

Goals for Aquatic Therapy
The therapist who is not familiar with working with patients who are s/p hip surgery may set unrealistic goals. It is important to realize that exercise in water can be a powerful tool for the rehabilitation of hip dysfunction.

Goals that would be appropriate for this population include:

• Rehabilitation of traumatized tissues by applying graded and progressively more taxing stresses on injured tissue;
• Improvement in strength or prevention of muscle atrophy;
• Improvement in flexibility or prevention of contractures; Improvement in posture (upright stance through terminal hip extension);
• Improvement in ability to perform ADLs;
• Decrease in fatiguability;
• Improvement in exercise tolerance;
• Improvement in work tolerance or duration;
• Prevention of loss of cardiovascular fitness immediately after surgery;
• Decrease in complaints of pain;
• Improvement in gait parameters;
• Improvement in balance, reaction time, and safety during ambulation;
• Prevention of lower extremity blood stasis or clots.

Benefits of Aquatic Therapy
Therapists cannot choose to place patients in the water simply because they believe in the "power of the pool". It is important for therapists to demonstrate through documentation that they have a solid rationale for placing the s/p surgical patient in the water.

These reasons (known collectively as the "beneficial effects" of aquatic therapy) should be listed in the Assessment section of any documentation on the patient.

For example, the therapist who evaluates a patient who is 15 days s/p total hip arthroplasty may choose to place the following statement in the initial evaluation.The following hydrodynamic and thermal effects of immersion and immersed activity make aquatic therapy the treatment of choice for this patient:

• Application of weight-bearing in a graded or progressive manner;
• Promotion of synovial fluid bathing of joints which decreases joint stiffness and pain;
• Promotion of circulation which promotes healing of musculoskeletal injuries; Retardation of muscle atrophy and contractures which may occur in the absence of exercise;
• Retardation of the loss in cardiovascular fitness which often accompanies surgery;
• Increase in proprioceptive awareness during exercise and functional task simulation;
• Application of resistance in a graded or progressive manner;
• Promotion of stretch of scarred tissue (s/p surgery);
• Assistance in limb movements against gravity (assisted by buoyancy);
• Reduction in joint compression forces during exercise;
• Decrease in muscle splinting and guarding from pain;
• Encouragement of socialization in a "normal" recreational environment.

Conclusion
As therapists who work in the water, you have the best of both worlds to offer patients with hip dysfunction. You see the possibilities inherent in gravity, yes; but you delight in the possibilities intrinsic to buoyancy, viscosity, turbulence and pressure. The universe expands: you can offer our patient air and water, an integration of effort and ease.

Disclaimer
The information presented in this article is meant to be a summary and educational in nature. It is not meant to serve as a substitute for legal advice.

Author Bio
Andrea Poteat Salzman, MS, PT is the owner of two businesses, the Aquatic Resources Network and Concepts in Physical Therapy. She has received both the prestiguous Aquatic Therapy Professional of the Year Award (Aquatic Therapy and Rehabilitation Institute) and the Tsunami Aquatic Therapy Award.

Salzman is well-regarded within the industry as:

• Editor-in-Chief of an aquatic therapy trade journal and newsletter;
• Author of over a dozen publications, including the soon-to-be-released Evidence-Based Aquatic Therapy textbook;
• Freelance author and columnist;
• Aquatic therapy seminar instructor;
• Adjunct faculty and research advisor, St. Catherine Physical Therapy Program, Minneapolis, MN;
• Immediate past manager of therapeutic aquatics, St. Paul Ramsey Medical Center, St. Paul, MN;
• Researcher and grant recipient examining aquatic exercise vs. land-based exercise.

She may be reached via e-mail at asalzman@aquaticnet.com